Advanced1

802.11 n and MIMO

802.11 n is a major improvement over previous models of 802.11 a/b/g. The new features are :-
1. Support for MIMO
MIMO uses multiple antennas for Tx and Rx using spatial multiplexing. Spatial multiplexing is multiplexing the same frequency channel using multiple antennas, each sending a part of the information to a receiver which also has multiple antennas listening on the incoming signal. Each antenna receives part of the signal and spatial signatures are taken into account to reconstruct the total signal using on-board DSP equipment. This is a major advance, in the sense that we have higher throughput without using TDM or FDM, which were the traditional ways of increasing throughput.

MIMO, of course, requires multiplicity of antennas at both sender and receiver. It should be noted that the Wireless Access Point (WAP) deals with one client at a time in a given frequency band ( there is dual band : 2.4 Ghz and 5 ghz support, which hence can deal with two clients simultaneously, but still having the restriction of having a single client per frequency band)

We tested MIMO throughput using a 802.11n capable WAP and Client to obtain the following interesting results:-

WAP is running licensed version of DD-WRT v24 and clients are running UNIX based Operating systems. We use iperf to measure TCP throughput between a iperf server initiated at the WAP and iperf client initiated at the client. It should be noted that, iperf measures TCP throughput, which will be lesser than the bandwidth or actual data transmitted which includes preambles, headers, etc.

Also, it should be noted that , we have obstructions in the path between the WAP and clients resulting in reduced SNR. But, over the set of experiments, these factors stay invariant, so we can do a reasonable comparison